1. Field of the Invention
The present invention relates to a fuel property judgement device used in an internal combustion engine, and more particularly to a fuel property judgement device for an internal combustion engine, which may rapidly determine fuel property at a starting operation with a high reliability to prevent a degradation of the controllability without increasing a cost.
2. Description of the Related Art
A fuel controlling system at the time of starting operation of an internal combustion engine (engine) or immediately after the start thereof is conventionally known which detects an engine coolant water temperature (engine temperature) and determines an amount of fuel at the time of the start in response to the engine temperature, or which determines an increment amount of fuel in response to the engine temperature at the time of starting operation and gradually decreases the fuel increment amount on the time basis immediately after the start.
Also, an ignition timing controlling system immediately after the start of the engine is conventionally known which controls the ignition timing on an angular advance side to the standard value in response to the detected engine temperature.
Furthermore, an idle air amount controlling system immediately after the start of the engine or during the engine starting period is conventionally known which determines an amount of air at the time of starting operation in response to the detected engine temperature or which determines an air amount increment value in response to the engine temperature at the time of starting operation operation and gradually decreases the air amount increment value on the time basis immediately after the start.
However, in such conventional internal combustion engine controlling systems, the fuel property is not particularly taken into consideration in the fuel amount control, the ignition timing control and the idle air amount control, and the fuel amount at the time of operation start and immediately after the start, the ignition timing and the idle air amount are selected to be optimized for matching the specific fuel property.
Also, in a conventional transient fuel controlling system for an internal combustion engine, an acceleration condition of the engine is detected from a change of throttle valve opening degree or a change of an air intake amount, a fuel supply rate is increased at the time of start of the acceleration by a acceleration increment means and thereafter -the acceleration increment amount is gradually decreased. At this time, the acceleration increment rate is variably set by using any of the intake amount, the throttle valve opening degree, the engine temperature, an engine rpm as a parameter.
In the same manner, a conventional ignition timing controlling system for an internal combustion engine is known which detects the acceleration condition of the engine from a change of a throttle valve opening degree or a change of an intake air amount and increases a delay angle at the time of ignition during the acceleration period.
However, in the same manner as described above, in such conventional internal combustion engine controlling systems, the fuel property is not particularly taken into consideration in the fuel amount control and the ignition timing control, the air/fuel ratio or the ignition timing during the transient state is selected to be optimized for matching the specific fuel property.
On the other hand, recently, an internal combustion engine controlling system which may always keep the stable combustion irrespective of the fuel property has been demanded. A variety of fuel property judgement devices that indirectly determine the fuel property has been conventionally proposed.
For instance, a case using heavy gasoline is exemplified as a complete example in which difference in fuel property raises a problem.
The heavy gasoline is gasoline whose extraction temperature is high, whose gasoline vaporization pressure (RVP) is low, and whose specific weight and octane value are high in comparison with regular gasoline.
However, there is no distinction between the heavy gasoline and the regular gasoline in standards. Also, there is no distinction in feeding at a gasoline station like the distinction between the regular gasoline and the high octane value gasoline.
Accordingly, there is a possible case where the heavy gasoline is fed to a vehicle installed with an internal combustion engine controlling system which performs the fuel amount control, the ignition timing control and the idle air amount control which are matched for the regular gasoline.
In the case where the heavy gasoline is fed to the above-described vehicle, the problem in travel is a hesitation in acceleration or instability in engine rpm at the time of starting operation and immediately after the start. Furthermore, impossibility of start of the engine or engine stop would occur, resulting in degradation in emission of exhaust gas.
The cause of the above-described disadvantage would be as follows. Due to the fact that the vapor pressure of the heavy gasoline is low and the fuel is stuck to the intake pipe so that a substantial fuel supply amount is decreased, the substantial air/fuel ratio is increased at the time of starting operation and immediately after the start, resulting in incomplete combustion.
Accordingly, as in, for example, Japanese Patent Application Laid-Open No. Hei 2-308945, a device for judging the fuel property on the basis of an engine cooling temperature (engine temperature) and a cranking time has been conventionally proposed.
However, according to the fuel property judgement device disclosed in the above-described publication, it is impossible to detect the fuel property during a period from the start of the stable rpm in accordance with a starter signal until the start of the engine itself.
Also, according to the fuel property judgement device disclosed in the above-described publication, when a voltage of a battery is lowered, there is a disadvantage that the rpm of the engine according to the starter signal is somewhat lower than that in the regular condition and the cranking time is prolonged more.
Also, as in, for example, Japanese Patent Application Laid-Open No. Sho 63-272935, as another fuel property judgement device, it is known to detect the fuel property from a period of the complete combustion at the time of starting operation at a low temperature.
Also, recently, a fuel property judgement device using a sensor for directly detecting the gasoline property has been developed. For example, as in, Japanese Patent Application Laid-open No. Hei 6-167474, it is known to use a static capacitance sensor utilizing a difference in specific induction ratio of the gasoline property and a gasoline temperature sensor.
Furthermore, as a fuel property judgement device using a gasoline property sensor, as in, for example, Japanese Patent Application Laid-Open No. Hei 6-81698, it is known to use a sensor utilizing a difference in refractive index of light due to the gasoline property.
However, such conventional devices suffer from a problem causing an increased cost, complication of components and a space problem of installation. Those devices are not always practical countermeasures.
As described above, according to each conventional fuel property judgement device for an internal combustion engine, the adverse affect of the difference in fuel property is not taken into consideration with respect to the controllability during a transient stage such as the start or acceleration in fuel amount control, ignition timing control and idle air amount control.
Accordingly, there is a fear that the engine would not be started at the time of starting operation of the engine for the fuel other than the specified fuel property. In addition, there are problems that the engine would be at an engine stop immediately after the start of the engine and the controllability would be considerably degraded at the transient operation of the engine.